Spark plug and method of making the same



NOV. 12, 1935. Q, Q RQHDE SPARK PLUG AND METHOD OF MAKING THE SAME Filed Feb. 9, 1934 2 Sheets-Sheet 1' v mw wwgamde 4 @WQQW O. C. ROHDE Nov. 12, 1935.

SPARK PLUG @flmW L W m UNITED STATES PATENT OFFICE SPARK PLUG AND METHOD OF MAKING O to C. Rohde, Toledo, pion Spark Plug Com poration of Delaware THE SAME Ohio, assignor to Champany, Toledo, Ohio, a cor- Application February 9, 1934, Serial No. 710,459

10 Claims.

This application relates to a spark plug and the method or making the same. More particularly it relates to a novel method of securing an electrode in a spark plug core and the structure resulting from this method.

Considerable difilculty has been encountered in the past in satisfactorily securing the central electrode in a spark plug core composed of porcelain or similar insulating material. The co-efficient of expansion oi the electrode is usually greater than that of the insulating material com posing the core, and its heat conductivity is usually greater. As a result the varying heat conditions to which the spark plug is subjected in use result in variations inthe relative sizes or the core and electrode. It is obviously diificult to maintain a secure and gas-tight connection between the core and the surrounding insulating material throughout these various relative changes in volume and without injury to the core.

The object of the present invention is to obviate these difliculties. The central idea of the invention is the use of a material to hold the electrode in place, which material may be introduced readily in powdered form and then compacted in place so as to form a secure holding body in gas-tight relation to the electrode and still capable oi yielding sufliciently to take up necessary relative difierences in volume of the electrode and core due to varying temperatures. A further object is to locate this holding body preferably in a position where it will be subjected to less violent temperature changes than the inner end of the core and also where the normal construction oi. the core provides considerable strength. Further details 0! the invention will appear asthe description proceeds. I

The invention will be described, first, as applied in several diilerent ways to a core of somewhat conventional iorm, and then the possible variations will be more fully disclosed.

In the accompanying drawings forming a part of this specification, Fig. 1. is a longitudinal section of a core having an electrode secured there in in accordance with one form of the invention;

Figs. 2 to 5, inclusive, aresimilar sections showing modifications in the application of the invention to the same electrode and core.

In the construction shown in the drawings there is a spark plug core I0 01 a widely used form. This core is provided with central bore having an upper end II somewha is customary, and a lower end I2 of about the usual diameter, that is, slightly larger than the diameter or the central electrode. Ashoulder II larger than is provided at the Junction of the bores 01 difierent diameters. The central electrode II has a shoulder or ring I! resting upon shoulder I3. The lower end I6 01 the central electrode extends below the core in the customary manner.

The parts thus far described are common to each of the views and, accordingly, these same reference numerals are applied on all the figures of the drawings.

In the form shown in Fig. l, the electrode is 10 secured in position by a securing body II. This is formed by introducing powdered soapstone or the like into the space between the electrode and the surrounding wall of bore II, and then compacting the powder to form a hard securing body, 16 which holds its place, grips the electrode and holds the electrode firmly in position, and forms a gas-tight joint therewith.

A sleeve I8 may be inserted above the compacted body II. Preferably the upper end I9 '0! the sleeve extends slightly above the upper end of the core and makes contact with a metallic cap 20 fitting over the upper end or the core and electrode. In this way good electrical connection betweenthe cap and the electrode is obtained. 25

The upper end of the core is not subjected to such violent variations in temperature as the lower end of the core and, thereiore,'th e electrode and sleeve. Il may fit bore I I fairly snugly without danger, but an excessively tight fit is not necessary. It will be readily recognized that the lower end of the electrode may fit somewhat loosely in bore I2 when the parts are cold so that the expansion of the electrode, when heated, does not unduly strain the lower end 01' the insulating core. The gas-tight seal is provided by body II.

It will be noted that in the construction shown,. body I! is substantially opposite the enlargement II, which is normally gripped externally in the 4 shell of the spark plug. The core is of largest diameter at this point and can best sustain any strains that are placed thereon by variations in the diameter of the electrode due to changing temperature conditions. At the same time this is 45 far enough from the firing end oi. the spark plug so as to. decrease the rapidity with which temperature changes occur.

Fig. 2 is similar to Fig. 1, except that it shows the entire bore I I filled with the compacted pow- 50 dered material Ih, which is similar to the securing body II described in connection with Fig. 1.

In Fig. 3 there is a similar construction except that the space within bore II above holding body I! is left empty. 01 course, suitable provision u is made or proper electrical contact with the upper end the electrode in this case.

Fig. 4 is similar to Figs. 1 and 3, except that the space within bore ll above holding body I! is filled with a powder 22, which may have any desired characteristics.

Fig. 5 illustrates a somewhat modified application of the invention. In this case there is shown within bore H, immediately above ring IS, a body of powder 23, which is refractory and need not be compactible so as to be readily pressed into a self-sustaining body. Above this powder 23 there is shown a compacted body l'lb similar to electrode-holding body l1.

This particular construction is suitable for use where the temperatures reached at the lower end of bore II are high enough to injuriously affect the material used for holding body ll When soapstone powder, or a similar material containing water of crystallization, is employed for the compactible powder, it might be injured by driving off the water of crystallization where the spark plug is subjected to excessive heat. Under usual working conditions the water of crystallization of soapstone is not given of! at temperatures reached by the main body of the spark plug core, but where the core is to be subjected to unusual heating conditions it may be desirable to raise the location of the electrode holding powder farther above the firing end, and the construction shown in Fig. 5 is one satisfactory way of accomplishing this purpose.

The powder used for body 23 may be anhydrous refrac ory material of any suitable kind or it may contain some water of crystallization where the proportion of such crystallized material is low enough so that any dehydration which occurs will not result injuriously.

Powdered soapstone or other magnesium silicate containing one molecule of water of crystallization to each molecule of the silicate is very suitable for the formation of holding body ll. Its structure is such that it may be readily fed into the space around the electrode in bore H and at the same time may be compacted therein by pressure so as to form a holding body securing the electrode in place and forming a substantially gas-tight joint therewith.

While powdered soapstone has been specified as particularly suited for this purpose, it will be understood that other powders may be employed provided they have the three necessary qualities, that is, suitability for easy feeding into the restricted space within the bore around the electrode, compactibility so as to form a holding body and sufiicient hardness to grip the electrode and hold it in place. As an incident to the compactibility, the powder should be suiiiciently compactible to make it substantially impervious to gas'. Furthermore, it must retain its holding and gripping properties and its imperviousness to gas when subjected to the heat which reaches it in its position within the spark plug.

While only one arrangement and location of the holding body within the core has been shown, it will be readily understood that suitable changes can be made in the construction of the insulating core and in the electrode and in the location of the holding body between the core and the electrode without departing from the main feature of the invention, which is the securing of the electrode in the core by means of 5 a compactible powder, which is compressed to form a holding body gripping the electrode, securing it in position in the core, forming a substantially gas-tight joint and constituting a body sufficiently yieldable to avoid injury to the structure because of the action of varying temperatures on materials having different degrees of expansion.

What is claimed is:-

l. The method of securing a central electrode in a ceramic spark plug core having a shouldered bore therein, which consists in inserting into the bore an electrode smaller in cross section than the larger portion of the bore, filling granular material into the bore around the electrode, and compacting the material in the bore against the shoulder thereof until it forms a self-sustaining body gripping the electrode and holding it in place.

2; A method in accordance with claim 1, and in which said material is a ceramic powder.

3. A method in accordance with claim 1, and in which the material is a ceramic powder that retains one molecule of water of crystallization to each molecule of the material until heated to a temperature above 800 F.

4. A method in accordance with claim 1, and in which said material is powdered talc.

5. A spark plug comprising an insulating core having a central bore with a shoulder therein, an electrode in the bore, and granular material compacted in the bore against said shoulder and gripping the electrode, holding it in place, and forming a substantially gastight joint therewith.

6. A spark plug in accordance with claim 5, and in which said material is ceramic powder.

7. A spark plug in accordance with claim 5, and in which said material is powdered talc.

8. A spark plug comprising an insulating core having a central bore therethrough, the bore at the firing end being smaller than at the other end, there being a shoulder between the different sized portions of the bore, a central electrode having a ring around it resting on said shoulder, fitting within the bore at the firing end when expanded by heat, and leaving a space therearound throughout the enlarged portion of the bore, and granular material compacted within the bore around the electrode and against said ring and shoulder, holding the electrode in place and making an air-tight joint therewith.

9. A spark plug in accordance with claim 8, and in which the material comprises powdered talc.

10. A spark plug in accordance with claim 8, and in which the material immediately in contact with the ring is refractory and substantial:- ly anhydrous, and the electrode-holding and gastight compacted powder is above said anhydrous powder.

OTTO C. ROHDE. 

